This is an old regional train coach, similar to the German n-Wagen, also known as Silberling. They were the backbone of Luxembourg's
regional train services in 1970s and 1980s, typically pulled by old French made electric locomotives. This one coach has been refitted
as a cafeteria wagon, but it is hardly ever in use.
Picture from the Luxembourg main station 17.12.2016 by Ilkka Siissalo.